172 lines
4.3 KiB
PHP
Executable File
172 lines
4.3 KiB
PHP
Executable File
<?php
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/**
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* Zend Framework
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*
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* LICENSE
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*
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* This source file is subject to the new BSD license that is bundled
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* with this package in the file LICENSE.txt.
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* It is also available through the world-wide-web at this URL:
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* http://framework.zend.com/license/new-bsd
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* If you did not receive a copy of the license and are unable to
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* obtain it through the world-wide-web, please send an email
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* to license@zend.com so we can send you a copy immediately.
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*
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* @category Zend
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* @package Zend_Search_Lucene
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* @copyright Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
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* @license http://framework.zend.com/license/new-bsd New BSD License
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* @version $Id: PriorityQueue.php 20096 2010-01-06 02:05:09Z bkarwin $
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*/
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/**
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* Abstract Priority Queue
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*
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* It implements a priority queue.
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* Please go to "Data Structures and Algorithms",
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* Aho, Hopcroft, and Ullman, Addison-Wesley, 1983 (corrected 1987 edition),
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* for implementation details.
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*
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* It provides O(log(N)) time of put/pop operations, where N is a size of queue
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*
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* @category Zend
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* @package Zend_Search_Lucene
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* @copyright Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
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* @license http://framework.zend.com/license/new-bsd New BSD License
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*/
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abstract class Zend_Search_Lucene_PriorityQueue
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{
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/**
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* Queue heap
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*
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* Heap contains balanced partial ordered binary tree represented in array
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* [0] - top of the tree
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* [1] - first child of [0]
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* [2] - second child of [0]
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* ...
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* [2*n + 1] - first child of [n]
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* [2*n + 2] - second child of [n]
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*
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* @var array
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*/
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private $_heap = array();
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/**
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* Add element to the queue
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*
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* O(log(N)) time
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*
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* @param mixed $element
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*/
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public function put($element)
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{
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$nodeId = count($this->_heap);
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$parentId = ($nodeId-1) >> 1; // floor( ($nodeId-1)/2 )
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while ($nodeId != 0 && $this->_less($element, $this->_heap[$parentId])) {
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// Move parent node down
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$this->_heap[$nodeId] = $this->_heap[$parentId];
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// Move pointer to the next level of tree
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$nodeId = $parentId;
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$parentId = ($nodeId-1) >> 1; // floor( ($nodeId-1)/2 )
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}
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// Put new node into the tree
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$this->_heap[$nodeId] = $element;
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}
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/**
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* Return least element of the queue
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*
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* Constant time
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*
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* @return mixed
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*/
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public function top()
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{
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if (count($this->_heap) == 0) {
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return null;
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}
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return $this->_heap[0];
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}
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/**
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* Removes and return least element of the queue
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*
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* O(log(N)) time
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*
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* @return mixed
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*/
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public function pop()
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{
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if (count($this->_heap) == 0) {
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return null;
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}
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$top = $this->_heap[0];
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$lastId = count($this->_heap) - 1;
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/**
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* Find appropriate position for last node
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*/
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$nodeId = 0; // Start from a top
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$childId = 1; // First child
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// Choose smaller child
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if ($lastId > 2 && $this->_less($this->_heap[2], $this->_heap[1])) {
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$childId = 2;
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}
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while ($childId < $lastId &&
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$this->_less($this->_heap[$childId], $this->_heap[$lastId])
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) {
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// Move child node up
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$this->_heap[$nodeId] = $this->_heap[$childId];
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$nodeId = $childId; // Go down
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$childId = ($nodeId << 1) + 1; // First child
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// Choose smaller child
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if (($childId+1) < $lastId
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&& $this->_less($this->_heap[$childId+1], $this->_heap[$childId])
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) {
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$childId++;
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}
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}
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// Move last element to the new position
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$this->_heap[$nodeId] = $this->_heap[$lastId];
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unset($this->_heap[$lastId]);
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return $top;
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}
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/**
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* Clear queue
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*/
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public function clear()
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{
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$this->_heap = array();
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}
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/**
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* Compare elements
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*
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* Returns true, if $el1 is less than $el2; else otherwise
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*
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* @param mixed $el1
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* @param mixed $el2
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* @return boolean
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*/
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abstract protected function _less($el1, $el2);
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}
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